1. Field of the Invention
The invention relates to a fuel control device, including an integral return fuel temperature diverter, to prevent cold clogging of the fuel filter media and also, modifications to improve air separation from the pressurized version.
2. Discussion of the Related Art
Fuel control devices are used in vehicle propulsion systems that use various fuels including diesel fuel. Stanadyne Corporation makes one example of a diesel fuel control device. These diesel fuel control devices can include an electric fuel pump and fuel pressure regulator. The electric pump and pressure regulator, modularly replace the hand primer pump, which has also been used in other fuel control devices.
Several diesel fuel filter system manufacturers have products that include optional electric fuel heaters. Under cold operating conditions, the electric fuel heater will warm the incoming fuel, preventing the formation of wax crystals on the fuel filter media that would otherwise have the effect of choking the filter media.
Diesel fuel systems have always had fuel returned to the fuel tank. Therefore the fuel supply flow is the sum of the fuel burned by the engine for power, plus the fuel flow returned to the fuel tank. As diesel fuel injection pressures have increased to meet modern emissions standards, the fuel injection systems have generated more heat and the fuel return flows have increased, as this fuel is now used for cooling the injection system. As the return flow increased, so did the supply flow. Under cold conditions, bigger electric fuel heaters were required to increase the fuel temperature to a level where wax would not form on the filter media. As the electric power for these heaters became difficult to manage, other methods of heating the supply fuel were initiated, including systems that used the heat in the return fuel.
Several diesel fuel filter systems have a return fuel temperature diverter system. The purpose of this diverter system is to permit the heat in the return fuel, to be used to raise the supply fuel temperature, to prevent wax formation on the filter media. However, once the engine warmed up and the return fuel became hot, it was then desirable to return it to the fuel tank directly. The return fuel diverter system then included a temperature sensitive component, such as a wax motor or bi-metal device, that would sense the temperature of the fuel supply and then provide activation for a diverter valve. If the temperature was low, then the warm return fuel was blended with the supply fuel. If the temperature was high, then the hot return fuel was diverted directly back to the fuel tank, sometimes through a fuel cooler.
The present invention combines the modular features of previous fuel control device systems with an integral temperature diverter system. Both a bi-metal disc and a wax capsule have been used to provide activation for the diverter valve. An electronic temperature sensor sending a signal to an electronic control module that activates a solenoid controlled diverter valve is also considered.
Under cold conditions, the temperature sensor permits the diverter valve to open, such that the return fuel is diverted to blend with the incoming supply fuel. The path back to the fuel tank is substantially blocked by a biased (loaded) check valve. Some leakage past the check valve is desirable (10% for example), to remove entrapped air from the system, as well as to provide some early heat for the return fuel system components.
Under hot conditions, the diverter valve is closed, mostly blocking the return fuel path to the supply side of the fuel filter. Some leakage past the diverter valve may be permissible (5% for example). Under these conditions, the biased check valve would open, permitting the return fuel to go back to the fuel tank. The biased check valve causes a minimal permissible back pressure in the fuel injection return system.
The diverter system was applied to two versions of a fuel control device. One version has an electric fuel pump and a fuel pressure regulator. The other version uses the mechanical fuel feed pump that is integral with the fuel injection system. This filter system incorporates a less expensive hand operated priming pump than is used to fill the system with fuel and purge any entrapped air, after a service event.
For the system that uses an electric fuel feed pump and a pressure regulator, this invention proposes adding a continuous air bleed orifice system, from the supply side of the fuel pressure regulator, to the fuel tank return fuel port in the fuel filter head. This air bleed purges any incoming air or vapor from the fuel supply system, back to the fuel tank. Otherwise, this air or vapor would only be able to leave through the fuel injection pump, which is undesirable.
The air bleed passage also includes a check valve in series with the orifice. In the event of an electric fuel pump failure, this check valve would prevent unfiltered fuel from being pulled along the fuel tank return line, by the mechanical feed pump that is integral with some fuel injection systems.